1. Field of the Invention
The present invention relates to improvements in a split type multicylinder internal combustion engine operable on less than all of its cylinders when the engine load is below a given value.
2. Description of the Prior Art
It is known that to increase the efficiency of a multicylinder internal combustion engine, the number of cylinders on which the engine operates under predetermined engine operating conditions can be reduced, particularly under conditions of low engine load. For this purpose, control means are provided which disable a number of cylinders in a multicylinder internal combustion engine by blocking the flow of air-fuel mixture to certain cylinders under low load conditions. The disablement of some of the cylinders of the engine increases the load on those remaining in operation and, as a result, the energy conversion efficiency is increased. It is common practice to block the flow of an air-fuel mixture to certain cylinders by closing a stop valve provided at the entrance of an intake passage which is connected to the certain cylinders and separated from the intake passage leading to the remaining cylinders.
One difficulty with such conventional split multicylinder internal combustion engines is that after the engine load exceeds a predetermined value and the stop valve opens, the disabled cylinders are held inoperative for the relatively long time it takes for the air-fuel mixture to reach the disabled cylinders through the associated intake passage. The result is poor engine acceleration performance.
The present invention provides an improved split multicylinder internal combustion engine which exhibits high engine performance particularly under acceleration with a greatly reduced time during which the engine operation is shifted from its split engine mode into its full engine mode after the engine load exceeds a predetermined value.